1. Field of the Invention
The present invention relates to an optical reader by which light reflected by an object is radiated on a sensor so that an image formed on the object is sensed. The optical reader is mounted in a copy machine, a facsimile machine and the like.
2. Description of the Related Art
In a conventional optical reader, a surface of an object to be read is illuminated by a light source such as an LED (light emitting diode). The light reflected by the object is focused on a CCD (charge coupled device) line sensor and the like by an imaging lens. Image information formed on the object is sensed by the line sensor. Signals corresponding to the image information are output from the line sensor, and transmitted to a signal processing unit.
In the conventional optical reader, the object is uniformly illuminated by the light source. Therefore, the amount of light received by the end portions of the line sensor is low in comparison with the center portion thereof due to a reduction in the amount of light passing through the imaging lens, in relation to the cos4 law. If the distribution of the amount of light in the optical image formed on the line sensor is non-uniform, the image information formed on the object can not be sensed with high accuracy.
To reduce the deviation in the light amount distribution, conventionally, there is a device in which a restriction plate is placed between the imaging lens and the line sensor, for example, so that the amount of light radiated on the center portion of the line sensor is reduced. In such a device, however, since an amount of light entering the line sensor is also reduced, the signal to noise ratio of an electric signal outputted by the line sensor is deteriorated. A precise image can not thus be sensed by the line sensor.
In another device, the amount of light provided by the light source (i.e., LEDs) is variable, and is controlled so that the amount of light at the center portion of the line sensor is reduced. However, such a device is complex and the manufacturing process is cumbersome.
Therefore, an object of the invention is to provide a light amount distribution control device which has a simple structure and causes a distribution of an amount of light received by a line sensor to become uniform without reducing the amount of light received by the line sensor, so that the image can be sensed with high accuracy.
According to the present invention, there is provided a light amount distribution control device, the device comprising light irradiating means and an elongated reflecting member reflecting light irradiated by the irradiating means to lead the light onto an object. A reflecting ratio of each portion of the reflecting member is changed along the longitudinal direction thereof.
Further, according to the present invention, there is provided an optical reader comprising a light source, an elongated reflecting member, an image forming optical system and reading means. In the reflecting member, a reflecting ratio is higher towards the ends of the reflecting member along the longitudinal direction of the reflecting member. Light irradiated by the light source is reflected by the reflecting member and illuminating an object to be read. The image forming optical system leads light reflected by the reflecting member and the object to an image plane. The reading means reads information formed on the object by sensing the light reflected by the reflecting member and the object. The reading means is provided on the image plane.